March 2015

To explain the origin of patience, scientists tell a modern-day fable. It is about cotton-top tamarins and their close cousins, marmosets.

Being patient often feels like a rational response, whereas being impatient feels like the animal mind acting out. Indeed, scientists used to think that the ability to be patient was a high-order function nearly unique to humans. Other animals were just impulsive, grabbing what they needed when they could get it.

But patience, it turns out, is more complicated than that. Research in the past decade suggests that all species have a combination of patience and impatience that makes sense for their evolutionary background.

The cotton-top tamarin and the marmoset provide evidence. Both new-world monkeys dine on tree gum. But they have different overall feeding strategies. The tamarins will eat the gum if they see it, but they’ll also eat other things like fruit and insects, foods that require a certain amount of impulsivity.

The marmosets, on the other hand, eat primarily the gum, using special teeth that let them gouge holes in a tree. “They basically just sit on the tree and wait for the sap to leak out of the tree and then they eat it,” says behavioral anthropologist Alexandra Rosati, who is finishing a postdoc at Yale before joining the faculty at Harvard. “As you can imagine, this is a very slow process.”

Noticing this ecological difference, Rosati’s colleagues including Jeffrey Stevens of the University of Nebraska-Lincoln tested the two monkeys to see how patiently they would wait for food. They did this by adapting a classic economics study, in which subjects are offered a small reward now or a larger reward later, in order to see how much they will discount the future reward. People who discount the future reward too much are considered to be acting irrationally.

For humans, the reward in this type of experiment is usually money, but Stevens offered the monkeys two versus six pieces of food. At first, he offered both with no delays. Of course, the monkeys preferred the six pieces to the two. Then he began delaying the six-piece option by a second, then two seconds, then three, and so on. Eventually, after the delay got long enough, the monkeys decided that it was better to have the two pieces now than the six pieces later.

As Stevens predicted, the tamarins and marmosets had a very different tolerance for waiting. For the tamarins, which forage impulsively for fruit and insects as well as tree gum, the game-changing delay was nearly 8 seconds on average. For the marmosets, which gladly wait for sap to ooze out of trees, the average delay was over 14 seconds.

This could mean that the marmosets are more rational than the tamarins. But the right conclusion (supported also by further research) seems to be the opposite one: That patience is not necessarily about rationality at all, but a finely tuned adaptation to ecological niche. “The amount of patience different species show is an evolved ability that is tailored to their normal environment,” Rosati says. That is, the marmosets' patience helps keep them alive; likewise, the tamarins' relative impatience helps keep them alive.

It follows that our inherited balance of patience and impatience must have kept our hunter-gatherer ancestors alive at one time too. The fact that today we value patience so much may indicate that that balance isn't working quite as well for us in the modern world. But if I had to give this fable a moral, it might be this: Patience is a virtue, but wait too long for anything and you might die.